The invention relates to an internal combustion with an adjustable compression ratio.
In conventional internal combustion engines, the position of the piston in the cylinder of the internal combustion engine depends exclusively on the position of the crankshaft. In other words, such internal combustion engines have a fixed compression ratio. Under certain operating conditions, however, it is be advantageous to have a variable compression ratio. Several concepts are known in this context.
In a particular embodiment of such internal combustion engines with a variable compression ratio, the connecting rod is divided into two parts, the relative position of which can be changed by means of a link arm in order to adjust the relative position between the piston and the crankshaft while changing the compression ratio. The disadvantage of such connecting rods is that they have a higher mass than known single-part connecting rods. This increases the moving mass of the engine, resulting in a higher load and weight.
Another known solution is the mounting of the crankshaft in eccentric supports, so that the crankshaft is displaceable relative to the crankcase. This, too, allows the position of the dead centers of the piston movement to be changed, so that an internal combustion engine with a variable compression ratio can be implemented. Such an internal combustion engine is for example known from DE 198 41 381 A1. Such systems have the disadvantage that, by changing the relative position of the crankshaft when adjusting the compression ratio, the position of the output shaft of the internal combustion engine is displaced as well. This requires complex structures for transmitting the drive torques from the internal combustion engine to further components of the drive train.
From EP 1 505 276 A1, an internal combustion engine with a variable compression ratio is known wherein the relative position between the cylinder block and the crankcase can be adjusted by means of an eccentric mechanism which comprises a plurality of eccentric elements mounted on a control shaft. Unfortunately, such a mechanism places a high load on the eccentric shaft arrangement mounted between the crankcase and the cylinder housing, which however requires a high strength structure of the crankcase for transmitting forces to the crankshaft and additional measures for the lubrication of the control shaft.
From EP 1 762 415 A1, an internal combustion engine is known which comprises an arrangement similar to that of EP 1 505 276 A1 for adjusting the compression ratio. For this purpose, the position of the cylinder housing relative to the crankcase can be changed by means of two eccentric shafts located in an upper section of the crankcase for moving the cylinder housing relative to the crankcase. In each case however the crankcase must be of a high strength design so as to be capable of transmitting the high forces effective during the compression and the power strokes of the engine between the cylinder head and the crankcase.
It is the object of the present invention to provide an internal combustion engine in which the distance between the cylinder head and crankshaft is adjustable in such a way that the compression ratio of the internal combustion engine can be adjusted by extremely simple means and without the need for a high-strength crankcase design.